(a) Field of the Invention
The present invention relates to a tap coupler. More specifically, the present invention relates to a tap coupler for extracting some of the optical signals transmitted from an optical transmission system.
(b) Description of the Related Art
A tap coupler of an optical transmission system extracts some of the optical signals flowing through optical paths and monitors states of the optical paths or the optical signals.
FIG. 1 shows a conventional tap coupler. As shown, the tap coupler comprises a collimator 1 and a beam splitter 2, that is positioned along an optical axis of the collimator 1 for reflecting some of the optical signals output from the collimator 1. One surface of the collimator 1 is coated with an antireflection coating.
In the above-noted tap coupler, the collimator 1 converts the optical signals transmitted via optical fibers into parallel beams and transmits the same to the beam splitter 2, and the beam splitter 2 permits some of the beams to penetrate with the remaining beams to be reflected. At this time, the quantity of beam signals reflected is varied according to a dividing ratio of the beam splitter 2, and the reflected beam signals are used to monitor the states of the optical transmission lines.
However, since the conventional tap coupler needs a beam splitter for extracting the optical signals for monitoring use, manufacturing cost is expensive. Also, since the beam splitter is used as well as the collimator, it is difficult to reduce the size of the tap coupler.
It is an object of the present invention to provide a tap coupler with smaller size and low manufacturing cost.
In one aspect of the present invention, a tap coupler comprises a ferrule comprising first and second optical fibers symmetrically positioned with respect to an optical axis for transmitting optical signals; and a graded index (GRIN) lens for converting a part of the optical signals provided by one of the optical fibers of the ferrule into parallel beams and outputting the same, and reflecting a part of the optical signals and outputting the same to another optical fiber of the ferrule with the GRIN lens having an uncoated beam outputting surface.
The GRIN lens can be arranged to be inclined to a predetermined angle with respect to the optical axis.
The GRIN lens can be arranged in order for the center of the GRIN lens to be over or below the optical axis.
An antireflection coating film is preferably formed on one surface of the GRIN lens facing the ferrule.
The distance between output ends of the first and second optical fibers and a beam outputting surface of the GRIN lens is preferably P/4, and the P represents one pitch of the optical signal.
The first optical fiber can be a single mode optical fiber and the second optical fiber can be a multi mode optical fiber.